In service, a load tap changing transformer is supplied with an input voltage and produces an output voltage. The purpose of a tap changer is to produce an output voltage that is well-regulated or stable despite fluctuations in the input voltage and load. The load tap changer has a number of spaced-apart output terminals and performs its regulatory function by adjusting the tap position so that, for a given input voltage, the output is taken from whichever tap yields an output voltage closest to the target level. The number of taps provided depends on the environment in which the tap changer is designed to operate and which is necessary to control the output voltage. The dynamic range of the tap changer is typically rated voltage plus or minus 10%. When the input voltage is at its rated value, and the tap changer tap position is in neutral, the output voltage of the transformer is at rated voltage. Operators of large industrial electrical installations utilizing transformers with tap changers need information about tap positions on the transformers because of the associated bearing on economy of operation, maintenance, safety, and system performance.
Various kinds of apparatus have been developed in the past for determining the tap position of a tap changer. These prior developments have culminated in standard electromechanical tap position indicators, or meters, that are physically attached as an add-on to the tap changer mechanism. The tap changer is typically a mechanical device that changes the tap position on a transformer by physically moving the contacts from one tap to another tap. The attached tap position indicator moves with the tap changer mechanism and displays the tap position on a dial or in some other conventional manner. A conventional electromechanical meter for displaying the tap position has drawbacks, such as producing only a local meter indication, which can be read by an operator only by going to the site of the meter. Furthermore, if meter readings are converted into a signal that can be transmitted to a remote location for reading or to a centrally located computer for processing, such conversion must be performed reliably and cost effectively if it is to be a viable tool.
Patents relating to the monitoring or determination of the tap position of a tap changer include U.S. Pat. Nos. 4,419,619, 4,612,617 and 5,119,012. U.S. Pat. No. 6,472,850 discloses a method and apparatus for determining a voltage regulator tap position. The devices and methods shown in these patents all have various drawbacks, including relative complexity and lack of applicability in retrofit situations.
In view of the foregoing, there is a need in the industry for a method and a system for efficiently and cost effectively monitoring load tap changes on a transformer. In addition, providing this information from a remote location and with a high level of accuracy would substantially meet the needs of utility companies for monitoring the tap movement range and real time position of remote tap changing transformers.